i have a live chat with representative of norton security and he says that
fire fox 20 is not compatible with norton identity safe and they are working
on it and check periodically and mean while there is no solution.

downgrading to an older version of Firefox is going to leave you open to attack from any of the dozen or so security holes patched in Firefox (and norton won't protect you from these attacks through the browser). It is not suggested or recommended. I would strongly suggest you move away from norton identity safe since they can't be trusted to stay up to date or modern, and find another program (or use Firefox's built-in password store) to keep your passwords. Staying on old, insecure programs is not wise at all